1. Technical Field of the Invention
The present invention relates to a mobile telecommunications network and, in particular, to the association of a uniform neighborhood list with a plurality of cell areas within a particular service area.
2. Description of Related Art
Within a cellular telecommunications system, a plurality of base stations each providing radio coverage over a particular geographic area are interconnected to form a system offering continuous and contiguous radio coverage. However, since a number of available or allocated radio frequencies or channels are fixed, the available frequencies or channels are accordingly planned and reused within a particular service area. As an illustration, an architecture having cells and clusters of cells is utilized to repeatedly reuse the available frequencies to provide radio coverage over a particular service area and to reduce co-channel interference created therewith.
While engaged in a call connection, a mobile station traveling within a particular mobile telecommunications network frequently moves out of a coverage area of a first base station and moves into a new coverage area being served by a second base station. As a result, unless the call is correctly and accurately transferred (handover) from the first base station to the second base station, the existing call connection is undesirably interrupted. Furthermore, mistakenly utilizing a frequency associated with a non-optimum cell by a mobile station further increases the level of co-channel interference created for a resulting air interface. It may further require an additional handover to improve the speech connection.
One of the ways for effectively handing over a mobile station from a first cell area to a second cell area is known as a mobile-assisted-handover (MAHO). A mobile station continuously measures signal strength from neighboring or adjacent base stations, reports the measurements back to the serving mobile telecommunications network, and assists in the handover between two adjacent base stations. Therefore, in order to enable a mobile station traveling within a particular cell area to measure beacon, pilot, control, or measurement frequencies associated with neighboring cells, the serving base station needs to identify a list of frequencies to be measured by the mobile station. Such a list is referred to as a "neighbor list", which is then continuously sent to mobiles after a call has been established. The mobile station then measures the identified frequencies to assist in determining whether a handover, for example, from the current cell area to one of the identified adjacent cell areas is needed.
A similar measurement is also made by a mobile station in idle mode as the mobile station roams from a first cell area, for example, to a second cell area. Such a process for selecting a new cell is referred to as a cell re-selection process. In this case the neighbor cell list broadcast on the control channel of the serving base station is specifying which channels to measure on.
Reference is now made to FIG. 1 which is a pictorial diagram of a service area 10 illustrating a plurality of cell areas each being served by a respective base station. Each base station is further associated with a measurement channel for identifying its coverage area. Such measurement channels are also known as beacon, control, page, and pilot channels. For exemplary purposes, only one measurement channel is shown assigned to each cell area in FIG. 1. But it will be understood that a plurality of channels, including traffic channels, are typically assigned to a single base station serving a particular cell area.
In a conventional manner, when a mobile station is located within a cell area being served by measurement channel number one 20, a base station associated with that cell area transmits a neighbor list identifying frequencies to be monitored by the mobile station. As an illustration, while being served by channel number one in cell 20, the associated base station instructs the mobile station to monitor and to measure signal strength associated with a neighbor list including measurement channel numbers two, three, four, five, six, and seven in cells 30, 40, 50, 60, 70, and 80, respectively. The transmitted neighbor list therefore instructs the mobile station to measure signals received over the indicated measurement channels from all possible cell areas into which the mobile station may possibly travel. Such a neighbor list is independently defined for (i.e., unique to) each cell. Accordingly, when the mobile station travels out of the current cell area 20 associated with measurement channel number one and into an adjacent cell area 40 being served by measurement channel number three, a base station serving the new cell area similarly transmits a new neighbor list instructing the mobile station to monitor a new set of measurement channels in neighboring cells. For example, while traveling within the cell area 40 associated with channel number three, the mobile station is similarly instructed to measure a neighbor list including measurement channel numbers eight, nine, ten, four, one, and two in cells 90, 100, 110, 50, 20 and 30, respectively.
However, such an implementation for providing a cell area dependent neighbor list is inconvenient and inefficient. During cell planning, for example, an operator or planner has to tediously define a plurality of neighboring frequencies or channel numbers for each cell within a particular network. Such an association may further require manual signal measurements within each of the associated cells to identify and to define a neighbor list. Furthermore, creating such a neighbor list in a certain environment may even be impractical. Such an environment, for example, includes man-made buildings or high-rises.
In order to effectuate a radio interface even within an enclosed environment, such as a building or high-rise, the concept of pico cells or indoor cells has been introduced. Reference is now made to FIG. 2 illustrating a building 200 being served by a plurality of base stations 210 located internally therein. Accordingly, when a mobile station enters the building 200, the mobile station effectuates mobile service by communicating radio signals with base stations (BSs) 210 strategically placed throughout the structure. Within such a three-dimensional layout, defining a customized neighbor list for each base station becomes very tedious and inconvenient. Furthermore, as furniture and walls are moved and/or rearranged, an associated neighbor list specifying the optimum neighboring channels may change. Moreover, due to interferences and fading, a base station located not adjacent to the current location may unexpectedly provide better radio communication to a particular mobile station than the most adjacent base station. As a result, the best cell candidate may not even be included within the provided neighbor list. Accordingly, within such a topography, a manually defined neighbor list may not provide the best channel candidate during a cell selection process for a mobile station.
Accordingly, there is a need for a mechanism to enable a serving mobile telecommunications system to select a better cell candidate for a traveling mobile station.